The proliferation of network computing has shaped how society transacts business andengages in personal communication. As reliance on computer networks grows, the flow of information between computers continues to increase in dramatic fashion. Accompanying this increased flow of information is a proportionate concern for network security. Commercial users, who regularly conduct business involving the exchange of confidential or company proprietary information over their computer networks, demand that such information is secure against interception by an unauthorized party or susceptible to corruption. In addition, with the acceptance of such applications as electronic commerce over the global Internet, all users recognize the critical role cryptographic systems play in maintaining the integrity of network communication.
The goal of cryptography is to keep messages secure. A message can be defined as information or data that is arranged or formatted in a particular way. In general, a message, sometimes referred to as “plaintext” or “cleartext”, is encrypted or transformed using a cipher to create “ciphertext,” which disguises the message in such a way as to hide its substance. In the context of cryptography, a cipher is a mathematical function that can be computed by a data processor. Once received by the intended recipient, the ciphertext is decrypted to convert the ciphertext back into plaintext. Ideally, ciphertext sufficiently disguises a message in such a way that even if the ciphertext is obtained by an unintended recipient, the substance of the message cannot be discerned from the ciphertext.
Many different encryption/decryption approaches for protecting information exist. In general, the selection of an encryption/decryption scheme depends upon considerations such as the types of communications to be made more secure, the particular parameters of the network environment in which the security is to be implemented, and the desired level of security. Since the level of security often has a direct effect on system resources, an important consideration is the particular system on which a security scheme is to be implemented.
For example, for small applications that require a relatively low level of security, a traditional restricted algorithm approach may be appropriate. With a restricted algorithm approach, a group of participants agree to use a specific, predetermined algorithm to encrypt and decrypt messages exchanged among the participants. Because the algorithm is maintained in secret, a relatively simple algorithm may be used. However, if the secrecy of the algorithm is compromised, the algorithm must be changed to preserve secure communication among the participants.
Scalability, under this approach, is a problem. As the number of participants increases, keeping the algorithm secret and updating it when compromises occur place an undue strain on network resources. In addition, standard algorithms cannot be used since each group of participants must have their own unique algorithm.
To address the shortcomings of traditional restricted algorithm approaches, many contemporary cryptography approaches use a key-based algorithm. Generally two types of key-based algorithms exist: symmetric algorithms; and asymmetric algorithms, of which one example is a public key algorithm. In a key-based algorithm, a key forms one of the inputs to a mathematical function that a computer or processor uses to generate a ciphertext.
Public key algorithms are designed so that the key used for encryption is different than the key used for decryption. The decryption key cannot be determined from the encryption key, at least not in any reasonable amount of time with practical computing resources. Typically, the encryption key (public key) is made public so that anyone, including an eavesdropper, can use the public key to encrypt a message. Only a specific participant in possession of the decryption key (private key) can decrypt the message.
Public key algorithms, however, often are not employed as a mechanism to encrypt messages largely because such algorithms consume an inordinate amount of system resources and time to encrypt entire messages. Further, public key encryption systems are vulnerable to chosen-plaintext attacks, particularly when there are relatively few possible encrypted messages.
As a result, a public key cryptosystem is utilized to establish a secure data communication channel through key exchanges among the participants. Two or more parties, who wish to communicate over a secure channel, exchange or make available to each other public (or non-secure) key values. Each party uses the other party's public key value to privately and securely compute a private key, using an agreed-upon algorithm. The parties then use their derived private keys in a separate encryption algorithm to encrypt messages passed over the data communication channel. Conventionally, these private keys are valid only on a per communication session basis, and thus, are referred to as session keys. These session keys can be used to encrypt/decrypt a specified number of messages or for a specified period of time.
A typical scenario involves exchanging a message between two users, or participants, A and B. User A is considered a publisher of a message to a subscriber, user B. The public key algorithm used to establish a secure channel between publisher, A, and subscriber, B, is as follows:                1. B provides a public key, B, to A.        2. A generates a random session key SK, encrypts it using public key B and sends it to B.        3. B decrypts the message using private key, b (to recover the session key SK).        4. Both A and B use the session key SK to encrypt their communications with each other.The above approach provides the added security of destroying the session key at the end of a session, thereby providing greater protection against eavesdroppers.        
A known public key exchange method is the Diffie-Hellman method described in U.S. Pat. No. 4,200,770. The Diffie-Hellman method relies on the difficulty associated with calculating discrete logarithms in a finite field. According to this method, two participants, A and B, each select random large numbers a and b, which are kept secret. A and B also agree (publicly) upon a base number p and a large prime number q, such that p is primitive mod q. A and B exchange the values of p and q over a non-secure channel or publish them in a database that both can access. Then A and B each privately compute public keys A and B, respectively, as follows:A privately computes a public key A as: A=pa mod (q)  (1)B privately computes a public key B as: B=pb mod (q)  (2)A and B then exchange or publish their respective public keys A and B and determine private keys ka and kb as follows:A computes a private key ka as: ka=Ba mod (q)  (3)B computes a private key kb as: kb=Ab mod (q)  (4)As evident from equation (3), A's private key is a function of its own private random number, a, and the public key, B. Likewise, equation (4) indicates that B's private key depends on its own private number, b, and the public key of A. As it turns out, A and B arrive at the shared secret key based upon the following:ka=Ba mod (q) and kb=Ab mod (q)Substituting for A and B using equations (1) and (2) above yields:ka=(pb mod (q))a mod (q) and kb=(pa mod (q))b mod (q)k=pba mod (q) and kb=pab mod (q)Therefore, ka=kb.
Using the Diffie-Hellman protocol, A and B each possesses the same secure key ka, kb, which can then be used to encrypt messages to each other. An eavesdropper who intercepts an encrypted message can recover it only by knowing the private values, a or b, or by solving an extremely difficult discrete logarithm to yield a or b. Thus, the Diffie-Hellman protocol provides a relatively secure approach.
FIG. 6 shows a broadcast version of the Diffie-Hellman method involving three clients, nodes or users A, B, C. Although three users are shown as an example, any number of clients, nodes or users may participate in the same approach.
Initially, each of the participants A, B, and C randomly generates private integers, a, b, and c, respectively. Thereafter, they compute their public keys, as in block 601, as follows:A=pa mod (q)  (5)B=pb mod (q)  (6)C=pc mod (q)  (7).Next, in block 603, user A sends message C′=Ca mod (q) to user B. In turn, B transmits the message, A′=Ab mod (q) to C, per block 605. User C sends A, as in block 607, the message B′=Bc mod (q). Lastly, the users arrive at a shared secret key, k, by computing the following:A computes k: k=B′a mod (q)=pabc mod (q)  (8)B computes k: k=C′b mod (q)=pabc mod (q)  (9)C computes k: k=A′c mod (q)=pabc mod (q)  (10)When it is used in a network environment comprising a plurality of network nodes, the Diffie-Hellman key-exchange algorithm requires N×(N−1) rounds of point-to-point unicast messages between logically adjacent member nodes. With three nodes, as in this instance, there are 6 total messages exchanged as each member node communicates its public key to the other members of the group. As the number of multicast group members grows, this method of key-exchange requires extensive message traffic and may introduce appreciable system delay.
One approach for improving the efficiency of public key exchange is presented in co-pending application Ser. No. 09/393,410, filed on the same date as this application, by the same named inventor, and entitled “OPERATIONAL OPTIMIZATION OF A SHARED SECRET DIFFIE-HELLMAN KEY EXCHANGE AMONG BROADCAST OR MULTICAST GROUPS.” This approach operationally optimizes key exchange and permits nodes in a network to carry out public key exchange using far fewer messages than the number of messages required in the Diffie-Hellman approach. However, an approach using a different computational method still is desirable.
Based upon the foregoing, there is a clear need for improved approaches to key exchange that minimize network processing delays, especially among broadcast or multicast group members in a network.
In particular, there is an acute need for an improved approach to enhance scalability.
Other needs and objects will become apparent from the following description.
Based on the need to provide secure communication while limiting the adverse effects on system resources and the limitations in the prior approaches, an approach for providing secure communication that provides a relatively high level of security while requiring relatively fewer system resources and time to perform is highly desirable.